This invention relates to a new and novel resealable pressure relief vent valve for use in connection with rechargeable cells and batteries. More specifically, the present invention relates to a resealable pressure relief vent valve which, upon the build up of pressurized gas within the cell or battery container, opens to discharge a portion of the gas to atmosphere and thereby relieve or reduce the pressure of the gas remaining in the container.
The present invention is particularly useful in connection with rechargeable nickel-cadmium cells and batteries. Nickel-cadmium cells incorporating a starved or limited amount of electrolyte are commonly classified as sealed cells. A sealed cell during normal operation does not require a release of gas within the cell to atmosphere. Rather, the cell functions through repetitive charge and discharge cycles as a closed system without any release of gas to the atmosphere. Hence, the cell is said to be sealed during normal operation. However, when a nickel-cadmium cell is subjected to abuse or malfunction, hydrogen and/or oxygen gas may be generated in the cell and may result in the build-up of high and excessive gas pressure. In these circumstances, it is desirable to relieve the pressure of the gas within the cell by providing a resealable vent. The resealable vent opens at a predetermined pressure to connect the cell interior to the atmosphere thereby permitting the discharge of a portion of the gas to the atmosphere and then, after the gas discharge, reseals the cell interior from atmosphere thereby permitting the cell to function as a closed system. While such a cell is permitted to vent as heretofore described the cell, nonetheless, is commonly referred to as a sealed cell.
Starved electrolyte nickel-cadmium cells are provided with a limited amount of electrolyte in order to function properly. Venting of gas from a nickel-cadmium cell often reduces the amount of electrolyte remaining in the cell since small droplets of electrolyte may become entrained in the gas exiting the cell. While a nickel-cadmium cell may be vented on an infrequent basis without exhibiting a significant performance loss, venting of the nickel-cadmium cell on a repetitive frequent basis will result in excessive electrolyte removal and attendant cell dryout. Upon cell dryout the cell ceases to function adequately. Said another way, the vent valve mechanism should open only upon those infrequent occasions when the gas pressure within the cell is excessively high due to malfunction or abuse of the cell. Otherwise damage to the cell will occur Accordingly, it is important that a vent mechanism be designed to operate to vent gas from the cell only on infrequent occasions of excessive pressure and to effectively reseal the cell after the venting of gas to the atmosphere.
Vent mechanisms for nickel-cadmium cells generally may be set to open at pressures between 200 to 400 psi. The choice of the vent opening pressure depends upon the basic mechanical design of the cell with the opening pressure of the vent usually set such that pressure relief will occur through the vent before the pressure build-up is sufficient to rupture the cell. However, virtually all vented nickel-cadmium cells permit the build-up of some pressure less than the rupture pressure of the cell. Therefore, the vent mechanism for nickel-cadmium cells must, in addition to having the capability of relieving excessive gas pressure from the interior of the cell, have the capability of effectively sealing the interior of the cell from electrolyte leakage while the cell is pressurized at pressures below the rupture pressure. Since even pressures below the rupture pressure may be significant, the sealing integrity of the vent mechanism must be sufficient to provide an effective seal under conditions of substantial pressure.
Vent mechanisms for nickel-cadmium cells frequently are comprised of a number of component parts. During assembly of the component parts into a completed mechanism, the various component parts may become misaligned whereby the sealing force or the vent opening pressure will be different from the intended sealing force and vent opening pressure found in vent mechanisms with properly aligned parts. In high volume production lines, the rapidity at which the vent mechanisms must be assembled increases the probability of misalignment of component parts and increases the probability of the presence of sealing forces and vent opening pressures at variance from intended sealing forces and vent opening pressures. This variance may result in a vent mechanism which permits venting of gas from the cell at a pressure less than that intended. Accordingly, the cell will vent more frequently than necessary and premature dry out of the electrolyte within the cell will occur. The variance may also result in a sealing force which is not sufficient to keep electrolyte from leaking from the cell under certain conditions when there is a substantial pressure within the cell container. Even though relatively little or no pressure may exist in the cell, nickel-cadmium cells are susceptible to a phenomenon commonly known as creep leakage which involves leakage of the electrolyte from the cell when the cell is inadvertently externally shorted. The present inventions provide a vent mechanism adapted to overcome all of the aforementioned problems.
It is therefore an object of the present invention to provide a resealable pressure relief vent valve for use in a rechargeable nickel-cadmium cell.
It is another object of the present invention to provide a resealable pressure relief vent valve which will relieve excessively high gas pressure within the rechargeable cell.
It is still another object of the present invention to provide a resealable pressure relief vent valve which will open only upon the infrequent occasions where the gas pressure within the cell is excessively high due to abuse or malfunctioning of the cell.
It is yet another object of the present invention to provide a resealable pressure relief vent valve which, after relieving the gas pressure within the cell, will reseal the interior of the cell from the atmosphere.
It is still yet another object of the present invention to provide a resealable pressure relief vent valve, for providing an effective seal against leakage of electrolyte from the cell, comprised of component parts which may be assembled at highly rapid rates without resulting in variances from required or intended sealing forces or vent opening pressures.